Tag: concentrated solar power

Posted on by

Energy storage in Spain

Spain’s Energy Landscape

In our previous post we reported on the prospects of energy storage in Denmark. Now we are moving back south. While it is commonly assumed that solar is the key driver of renewable energy production in Spain, wind represents more than three times the energy production than solar − Spain is a world leader in wind power. In 2014, Spain had the 4th most installed wind capacity, globally and wind energy accounted for 18% of total Spanish electricity production in 2015. Gas and coal still make up over one-third of electricity production in Spain.

Electricity Production in Spain (Source: International Energy Agency, 2015)

While fuel oil is still used for electricity in Spain, it should be noted that this is exclusive to the non-peninsular areas of Spain (i.e. Canary Islands, Balearic Islands, Cueta, Melilla, and several other small islands).

By 2020, 20% of Spain’s final energy consumption must come from renewable energy sources – as mandated in the 2009 EU Directive 28. However, Spain will likely miss this target. In the early 2000’s Spain was a global leader in renewable energy. For example, in 2005 Spain became the first country to mandate PV installations on all new buildings and ranked 5th globally in total renewable energy investments. However the renewable energy industry has stagnated significantly over the past decade. Unfortunately, Spain, which drove the global market in 2008, has virtually disappeared from the PV picture due to retroactive policy changes and new tax on self-consumption.

The policy changes and self-consumption taxes allude to the Royal Decree 900/2015 on self-consumption, a law enacted by the Spanish government in October 2015, which aims to financially penalize the self-consumption of electricity. Under the new law solar PV producers (residential PV owners, for example) are required to not only pay a tax on the energy they self-consume, but also must pay the same transmission & distribution fees they would have paid on an equivalent amount of electricity purchased from the grid. In addition to these charges and taxes, owners of systems 100 kW and smaller – most residential system owners – are prohibited from selling excess electricity from the grid. Instead, they must give it to the grid for free. Furthermore, this law is retroactive; meaning existing PV systems must comply or face a penalty. Penalties under the self-consumption law range from as low as EUR 6-million up to a maximum of EUR 60-million – about twice the fine for leaking radioactive waste. The Spanish government see’s self-consumption as a risk to tax revenues at the current high electricity prices.

Spain is still the world leader in concentrated solar power capacity (2.5 MW). However, no new plants were constructed since and there are currently no new plants under construction or in planning.

Energy Storage Market Outlook – Spain

Although initial drafts of the “self-consumption” law had strict provisions against battery storage systems, the final version does permit energy storage systems – although under conditions that make them impractical. While owners of solar-plus-storage systems are subject to additional charges, they also cannot reduce the amount of power that they have under contract from their utility company.
At this point in time, it appears as if the self-consumption law has effectively halted any investment in renewable energy and/or energy storage projects in Spain.

(Jon Martin, 2019; Photo: Wikipedia)

Posted on by

Faster photoelectrical hydrogen

Achieving high current densities while maintaining high energy efficiency is one of the biggest challenges in improving photoelectrochemical devices. Higher current densities accelerate the production of hydrogen and other electrochemical fuels.

Now a compact, solar-powered, hydrogen-producing device has been developed that provides the fuel at record speed. In the journal Nature Energy, the researchers around Saurabh Tembhurne describe a concept that allows capturing concentrated solar radiation (up to 474 kW/m²) by thermal integration, mass transport optimization and better electronics between the photoabsorber and the electrocatalyst.

The research group of the Swiss Federal Institute of Technology in Lausanne (EPFL) calculated the maximum increase in theoretical efficiency. Then, they experimentally verified the calculated values ​​using a photoabsorber and an iridium-ruthenium oxide-platinum based electrocatalyst. The electrocatalyst reached a current density greater than 0.88 A/cm². The calculated conversion efficiency of solar energy into hydrogen was more than 15%. The system was stable under various conditions for more than two hours. Next, the researchers want to scale their system.

The produced hydrogen can be used in fuel cells for power generation, which is why the developed system is suitable for energy storage. The hydrogen-powered generation of electricity emits only pure water. However, the clean and fast production of hydrogen is still a challenge. In the photoelectric method, materials similar to those of solar modules were used. The electrolytes were based on water in the new system, although ammonia would also be conceivable. Sunlight reaching these materials triggers a reaction in which water is split into oxygen and hydrogen. So far, however, all photoelectric methods could not be used on an industrial scale.

2 H2O → 2 H2 + O2; ∆G°’ = +237 kJ/mol (H2)

The newly developed system absorbed more than 400 times the amount of solar energy that normally shines on a given area. The researchers used high-power lamps to provide the necessary “solar energy”. Existing solar systems concentrate solar energy to a similar degree with the help of mirrors or lenses. The waste heat is used to accelerate the reaction.

The team predicts that the test equipment, with a footprint of approximately 5 cm, can produce an estimated 47 liters of hydrogen gas in six hours of sunshine. This is the highest rate per area for such solar powered electrochemical systems. At Frontis Energy we hope to be able to test and offer this system soon.

(Photo: Wikipedia)

Posted on by

Better heat exchangers for concentrated solar power

Solar thermal systems are a good example of the particle-wave dualism expressed in Planck’s constant h: E = hf. Where h is the Planck constant, f is the frequency of the light and E is the resulting energy. Thus, the higher the frequency of the light, the higher the amount of energy. Solar thermal metal collectors transform the energy of high-frequency light by generating them to an abundance of low-frequencies through Compton shifts. Glass or ceramic coatings with high visible and UV transmittance absorb the low frequency light generated by the metal because they effectively absorb infrared light (so-called heat blockers). The efficiency of the solar thermal system improves significantly with increasing size, which is also the biggest advantage of such systems compared to photovoltaic generators. One disadvantage, however, is the downstream transformation of heat into electricity with the help of heat exchangers and turbines − a problem not only in solar thermal systems.

To provide the hot gas (supercritical CO2) to the turbines, heat exchangers are necessary. These heat exchangers transfer the heat energy generated by a power plant to the working fluid in a heat engine (usually a steam turbine) that converts the heat into mechanical energy. Then, the mechanical energy is used to generate electricity. These heat exchangers are operated at ~800 Kelvin and could be more efficient if the temperature were at >1,000 Kelvin. The entire process of converting heat into electricity is called a power cycle and is a critical process in power generation by solar thermal plants. Obviously, heat exchangers are pivotal elements in this process.

Ceramics are a great material material for heat exchanger because they can withstand extreme temperature fluctuations. However, unlike metals, ceramics are not easy to shape. Relatively coarse shapes, in turn, are made quickly and easily. In contrast, metals can be easily formed and have a high mechanical strength. Metals and ceramics have been valued for centuries for their distinctive properties. For example, bronze and iron have good impact resistance and are so malleable that they have been made into complex shapes such as weapons and locks. Ceramics, like those used to make pottery, have been formed into simpler shapes. Their resistance to heat and corrosion made ceramics a valued material. A new composite of metal and ceramic (a so-called cermet) combines these properties in amazing ways. A research group led by Mario Caccia reported now in the prestigious journal Nature about a cermet with properties that makes it usable for heat exchangers in solar thermal systems.

The history of such composites goes back to the middle of the 20th century. The advent of jet engines has created a need for materials with high resistance to heat and oxidation. On top of that, they had to deal with rapid temperature changes. Their excellent mechanical strength, which often surpassed that of existing metals, was highly appreciated by the newly created aerospace industry. Not surprisingly, the US Air Force funded more research into the production of cermets. Cermets have since been developed for multiple applications, but in most cases have been used for small parts or surfaces. The newly released composite withstands extreme temperatures, high pressures and rapid temperature changes. It could increase the efficiency of heat exchangers in solar thermal systems by 20%.

To produce the composite, the authors first produced a precursor, which was subject to further processing, comparable to potting the unfired version of a clay pot. The authors compacted tungsten carbide powder into the approximate shape of the desired article (the heat exchanger) and heated it at 1,400 °C for 2 minutes to bond the parts together. They then further processed this porous preform to produce the desired final shape.

Next, the authors heated the preform in a chemically reducing atmosphere (a mixture of 4% hydrogen in argon) at 1,100 °C. At the same temperature, they immersed the preform in a tank of liquid zirconium and copper (Zr2Cu). Finally, the preform was removed by heating to 1,350 °C. In this process, the zirconium displaces the tungsten from the tungsten carbide, producing zirconium carbide (ZrC) as well as tungsten and copper. The liquid copper is displaced from the ZrC matrix as the material solidifies. The final object consists of ~58% ZrC ceramic and ~36% tungsten metal with small amounts of tungsten carbide and copper. The beauty of the method is that the porous preform is converted into a non-porous ZrC / tungsten composite of the same dimensions. The total volume change is about 1-2%.

The elegant manufacturing process is complemented by the robustness of the final product. At 800 °C, the ZrC / tungsten cermet conducts heat 2 to 3 times better than nickel based iron alloys. Such alloys are currently used in high-temperature heat exchangers. In addition to the improved thermal conductivity, the mechanical strength of the ZrC / tungsten composite is also higher than that of nickel alloys. The mechanical properties are not affected by temperatures of up to 800 ° C, even if the material has previously been subjected to heating, e.g. for cooling cycles between room temperature and 800 °C. In contrast, iron alloys, e.g. stainless steels, and nickel alloys loose at least 80% of their strength.

(Photo: Wikipedia)